Fig. 2.

Na⁺ currents in nucleated patches inactivate rapidly and are blocked by TTX. A, Voltage-gated Na⁺ currents evoked by 50 mV, 5 msec depolarizations. Command potentials are shown above the current responses. The first (large) and fifteenth (small) responses in a train of step depolarizations (20 Hz) are superimposed, revealing the current reduction attributable to cumulative, prolonged inactivation. The response in the presence of 0.5 μm TTX is also superimposed. Imperfect capacitive transient subtraction is apparent at the beginning and end of the responses. Each current trace is an average of 24 trials. B, The same data as inA, but with the fifteenth response scaled (dotted line) to match the peak amplitude of the first response, revealing the similar time course of fast inactivation.C, Similar data as in A, but from a different nucleated patch, and in response to 50 mV, 2 msec depolarizations. Each current trace is an average of six trials.D, Data in C, with the fifteenth response scaled (dotted line) to match the peak amplitude of the first response.